[theman6660]

Fixes #315

Literal descriptions currently render Boolean values as Python True/False and omit legal null values. Clients relying on the schema description can consequently construct invalid GraphQL input or incorrectly reject null.

• Render Boolean members as true/false, preserving string and numeric members.
• Preserve nullability from Literal members and Optional/union wrappers when constructing descriptions, including through existing list unwrapping.
• Keep literal_allowed_values' public return contract unchanged.
• Cover helper behavior, entity introspection, and compose argument/input/output descriptions.

The helpers now live in graphql/type_mapping.py and are shared by both schema paths, so the fix is made there rather than in compose_schema.py.

Validation (Python 3.12.14):

• New/updated regression checks before the fix: 8 failed, 30 passed.
• python -m pytest tests/graphql tests/use_case -q: 424 passed, 2 skipped.
• git diff --check: passed.

AI-assisted implementation. No claim of validation on other Python versions or of running the repository-wide suite.

[allmonday]

thanks for your contributation